1. Field of the Invention
This invention relates to a signal recording medium and a disc cartridge holding this signal recording medium.
2. Description of Related Art
Up to now, a signal recording medium, having the major surface of a flexible disc substrate as a signal recording surface and adapted for recording information signals on this signal recording surface, such as a magnetic disc, has been in use.
As a magnetic disc employing a flexible disc substrate, such a disc having the diameter of 3.5 inch is in use. This magnetic disc has a center hub for chucking the magnetic disc to a disc drive device. The magnetic disc, used so extensively, has a recording capacity of 2 megabyte (MB).
The magnetic disc 200, now in wide use, has a disc substrate 201 of a flexible synthetic resin material, with the major surface of the disc substrate being used as a signal recording surface, as shown in FIGS. 1 and 2. The disc substrate 201 has a circular center opening 201a which is closed by a hub 202.
This hub 202 is formed of a magnetic material, such as iron, and has a tubular projection 202a fitted in the center opening 201a, and is mounted on the disc substrate 201 by having a flange 202b on the outer rim side of the projection 202a bonded to the rim of the center opening 201a, as shown in FIG. 2. At the center of the hub 202 is formed a rectangular spindle opening 202b passed through by a spindle 221 of a rotation driving unit 220 provided on the disc drive device as shown in FIG. 3. At a position of the hub 202 offset from a driving pin 223 on the disc drive device is bored a rectangular driving pin engagement opening 202c engaged by a driving pin 223 on the disc drive device. That is, the driving pin engagement opening 202c is formed at a pre-set distance from the spindle opening 202b.
The spindle opening 202b, provided in the hub 202, substantially has the shape of a square each side being sized to be slightly larger than the diameter of the spindle passed therein. This spindle opening 202b has its center C1--C1 offset towards the driving pin engagement opening 202c with respect to the center O2--O2 of the hub 202, as shown in FIG. 2. The spindle opening 202b is formed in the course of drawing the magnetic material of the hub 202 and has an upstanding wall section 202f on each side, as shown in FIG. 2. These upstanding wall sections 202f support the peripheral surface of the spindle 221 passed through the spindle opening 202b and functions to permit the spindle 221 to pass through the spindle opening 202b. The corners of the substantially square-shaped spindle opening 202b are arcuately formed, as shown in FIG. 1.
The hub 202, mounted on the disc substrate 201, has the distal end face of the projection 202a, in which are formed the spindle opening 202b and the driving pin engagement opening 202c, as a setting surface 202e for a disc supporting surface 222a of a disc table 222 of the disc rotation unit 220. The outer rim side of the setting surface 202e is used as a suction portion by a magnet 224 arranged on the outer rim side of the disc supporting surface 222a.
The magnetic disc 200, arranged as described above, is rotated in unison with the disc table 222 of the disc rotation unit 220 provided on the disc drive device side, as the hub 202 is checked and centered with respect to the disc table 222. The information signals are recorded or reproduced for the magnetic disc 200 by the magnetic disc 200 being operated by a magnetic head.
The disc rotation unit 220, provided on the disc drive device, on which is loaded the magnetic disc 200, has the disc table 222 integrally mounted on the distal end of the spindle 221 run in rotation by a spindle motor, not shown, as shown in FIG. 3. The upper surface of the disc table 222 mounted on the distal end of the spindle 221 is a disc supporting surface 222a on which is set the hub 202 of the magnetic disc 200. On the disc table 222 is mounted a driving pin 223 at a position offset from the spindle 221. The driving pin 223 is mounted for movement in a direction emerging from or receding into the disc supporting surface 222a and in a direction towards and away from the disc supporting surface 222a. The driving pin 223 is biased by biasing means, not shown, in a direction away from the spindle 221.
On the disc supporting surface 222a of the disc table 222 is arranged a ring-shaped magnet 224, such as a rubber magnet, arranged for surrounding the disc supporting surface 222a. The magnet 224 is mounted on the disc table 222 so that the magnet is lower in level than the disc supporting surface 222a on which is set the hub 202 of the magnetic disc 200 so that a pre-set distance H0 is maintained between the magnet surface and the setting surface 202e of the hub 202 set on the disc supporting surface 222a.
The magnetic disc 200 is chucked on the disc table 222 by having the spindle 221 passed through the spindle opening 202b, engaging the driving pin 223 in the driving pin engagement opening 202c, setting the setting surface 202e on the disc supporting surface 222a of the disc table 222, as shown in FIG. 4 and by having the hub 202 attracted by the magnet 224.
The state in which the magnetic disc 200 is loaded on the disc table 222 is hereinafter explained.
In an initial state in which the magnetic disc 200 is set on the disc table 222 and the spindle 221 is passed through the spindle opening 202b with the driving pin 223 engaging in the driving pin engagement opening 202c, the spindle 221 and the driving pin 223 are usually inserted into or engaged with the spindle opening 202b and the driving pin engagement opening 202c without being thrust from the inner peripheral surface of the spindle opening 202b or the driving pin engagement opening 202c. At this time, the center-to-center distance F between the spindle 221 and the driving pin 223 is an initial state distance for which the driving pin 223 is not moved towards the outer rim of the magnetic disc 200.
The spindle opening 202b is formed as a square-shaped opening having the length of each side equal to L and having arcuately rounded corners, as shown in FIG. 5. The spindle 221, inserted into the spindle opening 202b, is formed as a column having a diameter .phi.E shorter than the length D of one each side of the spindle opening 202b. The driving pin engagement opening 202c is formed as a rectangle having a length of a long side and a length of a short side equal to A and B, respectively, and arcuately rounded corners, as shown in FIG. 5. The driving pin 223, engaged in this driving pin engagement opening 202c, is formed as a column having a diameter .phi.C shorter than the length B of the short side of the driving pin engagement opening 202c.
If the disc table 222 is run in rotation in the direction indicated by arrow R in FIG. 5, from an initial state in which magnetic disc 200 is set on the disc table 222, with the spindle 221 passed through the spindle opening 202b and with the driving pin 223 engaged in the driving pin engagement opening 202c, as shown in FIG. 5, the driving pin 223 compresses against an outer corner of the driving pin engagement opening 202c disposed in the rotating direction of the disc table 222, as shown in FIG. 6, to shift the magnetic disc 200 towards the outer rim of the spindle 221. By the magnetic disc 200 being moved towards the outer rim of the spindle 221 by the driving pin 223, the spindle 221 is abutted on the corner of the driving pin engagement opening 202c of the spindle opening 202b remote from the corner of the driving pin engagement opening 202c on which is abutted the driving pin 223, as shown in FIG. 6, thus centering the hub 202 of the magnetic disc 200 with respect to the disc table 222.
When the hub 202 of the magnetic disc 200 is centered with respect to the disc table 222, there is produced a differential rotational velocity between the disc table 222 and the magnetic disc 200. That is, the driving pin 223 is rotated in advance of the magnetic disc 200 so that the driving pin 223 is abutted against the outer corner of the driving pin engagement opening 202c disposed along the rotational direction of the disc table 222. By the driving pin 223 compressing against the driving pin engagement opening 202c, the magnetic disc 200 is moved from the center towards the outer rim of the spindle 221 to center the hub 202 with respect to the disc table 222. At this time, the driving pin 223 is moved towards the inner rim of the hub 202 so that the center-to-center distance G between the spindle 221 and the driving pin 223 becomes smaller than the initial distance F shown in FIG. 5.
By the magnetic disc 200 being attracted to the disc table 222 by the magnet 224, the magnetic disc 200 is rotated in unison with the disc table 222 in the centered state. By the magnetic head scanning the signal recording area of the magnetic disc 200 in this state, the information signals can be recorded or reproduced for the magnetic disc 200.
The magnetic disc 200, arranged as described above, is housed in a main cartridge body portion 213 to form a disc cartridge 210, as shown in FIGS. 7 and 8. The magnetic disc 200 is loaded on the disc drive device as the magnetic disc is held in the main cartridge body portion 213 and chucked on the disc table 222 of the disc rotation unit 220.
The disc cartridge 210, holding the magnetic disc 200, is provided with the main cartridge body portion 213, produced by abutting and interconnecting an upper cartridge half and a lower cartridge half, and the magnetic disc 200 is rotatably housed within this main cartridge body portion 213. At a mid portion on the lower surface of the main cartridge body portion 213 is formed a spindle opening 215 into which is inserted the spindle 211, as shown in FIG. 8. In the facing upper and lower surfaces of the main cartridge body portion 213 are formed rectangular recording and/or reproducing apertures 221, 222. These apertures 221, 222 are disposed at a mid position in the left-and-right direction of the main cartridge body portion 213, and are formed from the vicinity of the spindle opening 215 towards the front side of the main cartridge body portion 213. The magnetic disc 200 accommodated in the main cartridge body portion 213 has its signal recording area partially exposed via the apertures 221, 222 across the inner and outer rims of the disc. There is also provided in the main cartridge body portion 213 a mistaken recording inhibiting hole 231 operating as a discriminating hole indicating whether or not the information signals recorded on the magnetic disc 200 held therein can be erased by overwriting or erasure. There is also provided in the lower surface of the main cartridge body portion 213 in register with the mistaken recording inhibiting hole 231 a disc discriminating hole 232 specifying the sort of the magnetic disc held in the main cartridge body portion 213, as shown in FIG. 8. By detecting this disc discriminating hole 232, it can be discriminated that the magnetic disc 200 held in the main cartridge body portion 213 is of the recording capacity of 200 MB. The disc discriminating hole 232 is provided in the disc cartridge 210 holding the magnetic disc 200 with the recording capacity of 2 MB.
On this disc cartridge 210 is mounted a shutter member 214, formed by an metal plate of aluminum or stainless steel or molded from a synthetic resin material, and which is adapted for opening/closing the recording and/or reproducing apertures 221, 222 from the front side of the main cartridge body portion 213 while being movable in a direction of opening/closing the recording and/or reproducing apertures 221, 222. The shutter member 214 has shutter portions 214a, 214b overlying the apertures 221, 222 and having apertures 233, 234 registering with the apertures 221, 222 when the shutter member has moved to a position opening the apertures 221, 222.
The magnetic disc with the diameter of 3.5 inch has a recording capacity of 2 MB. For processing a program software or data of a larger capacity, it is desired to furnish a magnetic disc of a higher recording capacity.
On the other hand, the magnetic disc having the diameter of 3.5 inch is in widespread use as a recording medium for an information processing apparatus such as a computer. Thus, it is desirable that the magnetic disc having the diameter of 3.5 inch shall be usable with interchangeability on a disc drive device having a magnetic disc of a high recording capacity.
The conventional magnetic disc, having the diameter of 3.5 inch, is run in rotation at 300 rpm for recording and/or reproducing information signals, has a drawback that it is low in the data transfer rate.